The ISG has performed and published a comprehensive and top-level analysis of the data collected by the Randomised Badger Culling Trial (RBCT) and associated studies. However, we consider further insights would accrue from a descriptive spatial-temporal representation of the data and sequence of events during the RBCT. In particular, we need further insights into the mechanism by which culling may increase herd breakdowns and how this may be ameliorated.
Our first aim is to produce an archive of data pertaining to the reactive component of the trial that will include data collected as part of the trial and existing data sets maintained by the VLA, Defra and Animal Health. This will be supplemented with environmental data such as climate and landscape features, census data and Geographical Information System (GIS) databases including satellite imagery and aerial photography (objective 1). This archive will be used to construct a web-based interactive GIS mapping tool for the visualisation of the RBCT reactive data that will display and summarise the data collected in the reactive component of the RBCT in a collection of maps layering information that can be explored interactively.
We propose to then use this GIS tool to assist in the epidemiological analysis of the reactive trial areas. The location, timing and severity of infections in cattle herds will be evaluated in relation to the location, timing and intensity of badger culling during the trial. We will perform descriptive epidemiological analyses to describe the sequence of events and the spatial and temporal relation between a confirmed Bovine Tuberculosis breakdown (CHB) on a farm, its associated culling operation and the distribution of subsequent breakdowns, incorporating badger activity, infection status and cattle and badger genotype information (objective 2). As part of this we will extend previous work at the VLA to estimate the temporal relation between culling and subsequent breakdowns in the nearest herds and contiguous herds.
Within trial areas there were holdings that experienced a breakdown and holdings that did not. The visual representation of the reactive areas and data archive will be used to identify factors that may affect the risk of breakdowns such as farm management factors and landscape and environmental factors that may affect exposure to badgers. Novel information about landscape factors such as length of boundaries, location of crops etc., will be extracted from the maps and utilised in a comparative epidemiological analysis to identify factors that may reduce the risk of a CHB (objective 5).
In addition, the wealth of data collected during the RBCT presents a unique opportunity to assess the importance of other factors that may greatly contribute to Bovine Tuberculosis control. In objective 3 we will attempt to identify factors that determine whether a unconfirmed breakdown will eventually be confirmed as truly infected with Mycobacterium bovis and assess the contribution of unconfirmed breakdowns to the epidemiology of bTB in all RBCT areas. In objective 4 the relationship between the monthly pattern of the number of reactors for breakdowns and the most likely source of infection will be estimated.
The research described will build on the knowledge base gained from SPIDA (a web based interactive mapping tool developed at the VLA) and could also be viewed as a pilot for how environmental, landscape and disease data might be combined to inform control strategies. It will enhance the RBCT data archive providing an extensive array of new environmental variables in the reactive area for current and future research. The epidemiological analyses proposed will provide a better understanding of how spatial and temporal factors effect the incidence of confirmed and unconfirmed breakdowns, and the effects of culling on a small scale.